This invention relates generally to the field of active, efficient, silicon-based photonic devices and photonic integrated circuits that are capable of monolithic integration with Si and SiGe electronics. The present invention does not include group III-V and II-VI photonic structures that are hybrid integrated onto silicon; instead, the present invention teaches an “all-group-IV” solution to the problem of active Si-based photonics in which the active strained-layer region consists of binary and/or ternary group IV alloy layers and/or Ge.
The Si-based photonic components and circuits in this invention are valuable for guided-wave and free-space applications. In the guided-wave case, the active devices taught here can merge with undoped silicon waveguides made from SOI and SOS, waveguides that transmit light over a very wide range of wavelengths because of silicon's transparency. This wavelength range begins at 1.2 μm and extends out to 100 μm. The 1.5-100 μm range is covered in this invention.
The prior art of active strained-layer Si-based photonics consists of SiGe/Si heterostructures and a few examples of GeSn alloy films grown upon a germanium substrate. The only prior-art patent we are aware of is the one by Soref and Friedman, U.S. Pat. No. 5,548,128, which describes Sn1-xGexSn1-yGey heterostructures. All the claims of that patent use SnxGe1-x as the quantum well active layers wherein the tin content is 5 to 15%, never zero. The claims in that patent do not include tensile-germanium layers within the active-layers-stack, that is, the barriers are GeSn, never Ge. This is a deficiency because elemental Ge is easy to deposit in a heteroepitaxial structure, and because recent research shows that an MQW having tensile Ge barriers and compressive GeSn wells in alternating layers with Type I band alignment is an excellent means for obtaining direct-gap wells. In addition, recent work shows that tensile Ge forms a useful quantum well upon a relaxed SiGeSn buffer of proper composition Regarding strain-compensated devices, the prior patent does not discuss strain balancing with Ge layers in the MQW. The prior patent deals with waveguided devices. Free-space devices, described here, are omitted from the prior patent, which is another deficiency because free-space devices such as normal-incidence photodetectors and surface-emitting lasers, are important. There is prior photonic art on Ill-V alloy structures hybrid-integrated on silicon, but this hybrid integration approach is deficient because the Si-to-III-V lattice mismatch creates difficulty and complexity in processing, tends to make the resulting structures costly and lower in quality. The present invention teaches stable, strain-engineered monolithic integration of group IV alloys on silicon.